i7-4710HQ and mPCI-e 2.0

Hi, I have some questions about egpu.
My laptop is lenovo y50-70 with i7-4710HQ and maxwell 860m. I made some cooling upgrade and can run on 3.5 ghz all the time at 100% (on stress test max temp. is 78 C). In past I could run about 3.0 and temp. was 90 C. And the gpu has poor preformance for this cpu. So I am thinking about egpu.

I have only one PCI-e 2.0 x1(wifi), so bandwidth is 5 GT/s. How will eGPU work on this port? Will it make big diffrence than 860m(maxwell)? Or it will bottleneck a lot, because of the slow x1 PCI-e 2.0 slot?

I checked that 860m have PCI-e 3.0 x16 and max bandwidth is 8 GT/s. So difference is not that big?